1. Field of the Invention
The present invention is broadly concerned with an improved method and apparatus for the incorporation of added liquid or meltable solid components into heterogeneous materials. More particularly, the invention pertains to such methods and apparatus wherein the components and other starting materials are continuously passed in serial order through an extruder and a sonolation device.
2. Description of the Prior Art
The commercial-scale production of emulsified products is a common problem encountered by industry. For example, it is sometimes necessary to incorporate oils or lipids into heterogeneous materials such as grains. One way of accomplishing this is to use relatively large quantities of emulsifiers. While this does yield effective emulsions, emulsifiers are very expensive. In another example, it is also sometimes necessary to add liquid ingredients to highly viscous gel or paste products such as toothpastes. In the past, it has generally been necessary to produce such products in a batchwise manner, because of the difficulty of insuring product uniformity.
Extruders are well known devices adapted for production of an almost limitless number of products such as animal or livestock feeds, starches and pastas. Extruders include an elongated barrel having an inlet and a spaced outlet, with one or more elongated, axially rotatable flighted screws located within the barrel for moving materials along the barrel. The outlet end of the barrel is normally equipped with a restricted orifice die serving to create back pressure within the barrel and to form the extrudate into a desired shape. In many instances, extruders are used to simultaneously cook and form materials, and in such cases generate elevated temperatures and pressures. In other cases, extruders can be used at relatively low or even ambient temperatures as forming devices.
Sonolation devices have also been proposed in the past for assisting in the mixing of materials. Such sonolation devices are in the form of elongated, tubular units having an internal orifice and a tunable, blade-like member adjacent the orifice. In use, materials passing through the sonolation device are subjected to intense acoustic vibrations which tend to break up discrete liquid droplets within the material to achieve a more uniform and emulsified final product. Sonolation devices are described in U.S. Pat. Nos. 3,176,964 and 5,854,336, both of which are incorporated by reference herein.
The present invention provides improved methods and apparatus for the incorporation of liquid components into other materials so as to yield stable final products. Broadly speaking, the methods of the invention involve passing one or more starting ingredients into an extruder and adding other components to such ingredients to form a composite, so that the composite passes through the extruder outlet to give an extrudate. Thereafter, the composite extrudate is treated by subjecting it to acoustic vibrations in a sonolation device.
In preferred forms, the added components can be in liquid form (typically a lipid, oil or lipid- or oil-based material), or as meltable solids (i.e., those which melt during processing). Such added components may be added to the other ingredients within the extruder barrel. This is usually accomplished by injecting the added components into the barrel at a point at least midway along the length of the barrel, and preferably closer to the outlet end thereof than the inlet. While such barrel injection is preferred, the invention is not so limited; if desired, the added components can be initially incorporated into the other starting ingredients, and the combination can then be fed to the extruder.
The composite extrudate is continuously directed under pressure from the extruder to the sonolation device. In order to be most effective, the extrudate should not be collected or held for any significant period between extrusion and sonolation. Preferably, the extrudate should pass through a closed conduit between the extruder and sonolation device, and the time between extrusion and sonolation should not exceed about 1 minute, and preferably should be no more than about 20 seconds.
The final product emerging from the sonolation device is characterized by a uniform color and consistency, and is stable against rapid separation of materials. This is accomplished with the complete elimination, or at least substantial reduction, of emulsifiers or other similar ingredients.